1. Field of the Invention
The present invention relates to an optical scale that detects the relative angle and relative displacement between a scale and detection means. The present invention also relates to an optical encoder using the same.
2. Related Background Art
Rotary encoders and linear encoders have been used as angle detection sensors or position detection sensors. In particular, in the case where position detection with high resolution is required, an incremental optical encoder is used.
The incremental encoder is a measuring device for detecting a relative angle or a relative displacement by counting two incremental signals, as disclosed in Japanese Patent Application Laid-Open Nos. 2000-266567 and 2003-97975.
However, what can be detected by counting incremental signals is a relative displacement. Therefore, to enable position detection, a reference position signal related to an external coordinate system is needed.
It is possible to obtain such a reference position signal using separate external means.
On the other hand, there has been known an encoder that is adapted to output a datum position signal at a specific position in addition to incremental signals to provide a reference signal by the encoder itself. This datum signal is sometimes referred to as a reference signal or an original point signal.